How load only some node fields?

Question

entity.query service is very handy when it comes to finding nodes with specific field values. Unfortunately all it returns are entity IDs and revision IDs.

In case in which result set is big it's really inefficient to load whole nodes if only data from specific fields is needed.

In D7 it was possible for example to use field_attach_load() function which (thankfully) has been removed in D8, as detailed in Fields are no longer handled individually and are bound to an entity type. The problem is that Drupal change log references loadFieldItems() and doLoadFieldItems() of FieldableEntityStorageControllerBase class neither of which exists in current release of D8.

What is the Drupal 8 way of loading data for specific node fields only?

Answer 1

According to Acquia articles and specifically this:

In Drupal 7, we often accessed fields directly, using hooks to modify fields when they were loaded, changed, or saved. In Drupal 8, there is a focus on entities instead of fields. Because of this, if we want to modify fields we need to get the fields out of the entities.

So in Drupal 8 you can't directly access any fields without first loading the whole entity as the following example (taken from the Acquia article) demonstrates:

/**
* @var $entity \Drupal\Core\Entity\Entity
*/
$entity = $entity_storage->load($entity_id);


/**
* @var $field \Drupal\Core\Field\FieldItemList
*/
$field = $entity->get($field_name);

// We get the string value from the field.
$value = $field->value;

// Get the summary from a body field.
$summary = $body_field->summary;

$field->value = 'changed value';

Unfortunately the specific thing you want doesn't exist in the API. All field data is loaded in bulk via ContentEntityStorageBase::doLoadRevisionFieldItems, and the standard SqlContentEntityStorage doesn't contain any methods for extracting individual fields. If you haven't already done so, it might be worth benchmarking this to see if there's a real problem. A lot of work was done on the cache system for D8, things might not be as slow as you think.

Implementing this manually would be pretty easy, just re-implement SqlContentEntityStorage::buildQuery in a new service class and change it to only load data for the field(s) passed in as an arguments from the table mapping. But you don't get any cache goodness with that, which I suspect is at least part of the reason loading individual fields was removed in the first place.

Answer 2

I did some profiling with a query of 100,000 nodes, fetching the field myfield from all nodes of type mybundle.

Good: A dynamic query with addField()

$connection = \Drupal::database();
$query = $connection->select('node__field_myfield');
$query->condition('node__field_myfield.bundle', 'mybundle');
$query->addField('node__field_myfield', 'field_myfield_value');
$result = $query->execute();
$values = $result->fetchAll();

This runs in about 250 milliseconds.

Bad: An entity query with loadMultiple()

$query = \Drupal::entityQuery('node');
$query->condition('type', 'mybundle');
$node_storage = \Drupal::entityTypeManager()->getStorage('node');
$values = [];
$nids = $query->execute();
$nodes = $node_storage->loadMultiple($nids);
foreach($nodes as $node) {
  $values[] = $node->get('field_myfield')->getValue();
}

This took 3 minutes after a few repeated attempts when the cache was fully built. After a cache rebuild, it took more than half an hour.

Answer 3

In case in which result set is big it's really inefficient to load whole nodes if only data from specific fields is needed.

What is the Drupal 8 way of loading data for specific node fields only?

uh...ummmm....Views with a filter and/or fixed contextual filter with allow multiple values checkmarked...

Note: Drupal 8 comes with views by default.

Answer 4

Please create View/Reference/Block/Attachment with selected field. And Call that using contextual filter.

For example : http://localhost/project/admin/structure/views/view/view_machine_name/edit/your_block

            $nameshipped = 'view_machine_name'; // please check the url
            $viewshipped = views_get_view($nameshipped);
            $display_id_shipped = 'your_block';
            $viewshipped->set_display($display_id_shipped);
            //$viewshipped->set_arguments(array($all_con_id)); // if we need to use contextual filter.
            echo $html = $viewshipped->render();

Please use the above code where you want to implement.